BiologyCBSE Class 11 · Biological Classification

Kingdom Monera: Archaebacteria, Eubacteria and Mycoplasma

Updated 17 October 2026 · Fact-checked

Kingdom Monera contains all prokaryotes: bacteria, cyanobacteria, archaebacteria and mycoplasma. They have no nuclear membrane or membrane-bound organelles, mostly a cell wall of peptidoglycan (absent in mycoplasma), and reproduce mainly by binary fission. Archaebacteria live in harsh habitats; eubacteria include cyanobacteria and heterotrophs; mycoplasma are the smallest living cells and lack a cell wall.

Learn the four shapes: sphere, rod, comma, spiral. Notice the bacterial cell has a wall and a nucleoid with no membrane-bound nucleus.

Illustration drawn for QuestionBuddy.

Understand Kingdom Monera: Bacteria

Monera in brief. Bacteria are the sole members of Kingdom Monera. They are the most abundant micro-organisms, living in soil, water, air, inside and on other organisms, even in hot springs, deep ocean mud and ice. Cells are prokaryotic: no definite nucleus, no mitochondria or plastids; the genetic material is a naked circular DNA in the nucleoid.

Shapes. Four forms: coccus (spherical), bacillus (rod), vibrio (comma) and spirillum (spiral).

Archaebacteria. Special cell wall structure that helps them live in harsh conditions. Three groups:

Halophiles: salty areas.
Thermoacidophiles: hot springs (high temperature and acidity).
Methanogens: marshes and in the guts of ruminants (cows, buffaloes), where they produce methane (biogas) from dung.

Eubacteria (true bacteria). Rigid cell wall; a flagellum if motile.

Cyanobacteria (blue-green algae): photosynthetic autotrophs with chlorophyll a (similar to green plants); unicellular, colonial or filamentous; found in freshwater, marine or terrestrial habitats, sometimes forming blooms in polluted water. Some, such as Nostoc and Anabaena, fix atmospheric nitrogen in specialised cells called heterocysts.
Chemosynthetic autotrophs oxidise inorganic substances (nitrate, nitrite, ammonia) for energy and help recycle nutrients such as nitrogen, phosphorus, iron and sulphur.
Heterotrophic bacteria are the most abundant: decomposers, disease causers (cholera, typhoid, tetanus, citrus canker), useful in curdling milk, making antibiotics and fixing nitrogen in legume roots.

Reproduction. Mainly fission. Under unfavourable conditions some produce spores. Sexual reproduction is primitive: DNA transfer from one bacterium to another (conjugation, transformation, transduction, as the cells do not form gametes).

Mycoplasma. Completely lack a cell wall; the smallest living cells known; can survive without oxygen; many are pathogenic to animals and plants.

Gram staining. Bacteria are classified Gram positive or Gram negative depending on the cell wall response to the stain (a feature of the wall's structure).

Table: archaebacteria versus eubacteria. Cell wall: special (no typical peptidoglycan) vs peptidoglycan. Habitat: extreme vs wide. Example: methanogens vs cyanobacteria.

Draw and label: shapes of bacteria. Checklist: coccus, bacillus, vibrio, spirillum, each with a flagellum for motile forms. Title: 'Shapes of bacteria'.

Kingdom Monera: Bacteria: key facts

Shapes: $C occ u s ∣ B a c i l l u s ∣ V ib r i o ∣ S p i r i l l u m$; Sphere, rod, comma, spiral
Archaebacteria: $H a l o p hi l es (s a l t) ∣ T h er m o a c i d o p hi l es (h o t, a c i d i c) ∣ M e t han o g e n s (m e t han e)$; Harsh habitats
Smallest cell: $M y co pl a s ma = n oce l l w a l l ∣ s u r v i v es w i t h o u t o x y g e n$; Smallest living cells
Nitrogen fixers: Nostoc
Anabaena
in heterocysts; Cyanobacteria

How to answer Kingdom Monera: Bacteria questions

Questions ask to classify, differentiate or give examples.

1Name the group (archaebacteria, cyanobacteria, mycoplasma) from the clue (habitat, cell wall).
2Match habitat to type: salt, hot acidic spring or marsh gut.
3Link function to structure: heterocyst = nitrogen fixation; no wall = mycoplasma.
4For reproduction, state fission first, then spore formation and DNA transfer as the primitive sexual mode.
5Give one economic use and one harm when asked about importance.

Kingdom Monera: Bacteria in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Biogas plant

Suppose a village family runs a gobar-gas plant fed with cattle dung and finds it makes a combustible gas.

Which bacteria help, to which group do they belong, and where else do they live?

Try it first, then show the solutionSolution

The gas is methane, made by methanogens.
Methanogens are archaebacteria, which live in anaerobic places such as marshes.
They also live in the gut of cattle, which is why dung is a good starter.

Answer: Methanogens (archaebacteria), found in marshes and ruminant guts.

Memory hook: Dung plus methanogens gives methane.

Tricks to remember Kingdom Monera: Bacteria

Short memory aids. Say each one aloud once, then use it on a question the same day.

HTM
Archaebacteria: Halophiles, Thermoacidophiles, Methanogens.
Use it when: Naming the three groups
C-B-V-S
Coccus, Bacillus, Vibrio, Spirillum.
Use it when: Shapes
No wall, smallest
Mycoplasma has no wall and is the smallest.
Use it when: Mycoplasma facts

Kingdom Monera: Bacteria: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Shapes · 2 marks · Very short answerBoard level

Name the four shapes of bacteria with one-word descriptions.

Try it first, then show the solutionSolution

Coccus: spherical; bacillus: rod (1 mark).
Vibrio: comma-shaped; spirillum: spiral (1 mark).

Answer: Coccus, bacillus, vibrio, spirillum.

Example 2: Archaebacteria · 3 marks · Short answerBoard level

A culture from a salt pan, one from a hot acidic spring and one from marsh mud all contain archaebacteria. Name the group of each and the feature that lets them survive.

Try it first, then show the solutionSolution

They have a special cell wall structure, which suits harsh conditions (1 mark).
Halophiles in salty areas; thermoacidophiles in hot acidic springs (1 mark).
Methanogens in marshes and ruminant guts, producing methane (1 mark).

Answer: Special cell wall; halophiles, thermoacidophiles, methanogens.

Example 3: Cyanobacteria · 3 marks · Short answerHarder board level

Describe the structure and importance of cyanobacteria, with two examples.

Try it first, then show the solutionSolution

Prokaryotic photosynthetic autotrophs with chlorophyll a, unicellular, colonial or filamentous (1 mark).
Nostoc and Anabaena fix atmospheric nitrogen in heterocysts (1 mark).
They form blooms in polluted water and add organic matter and nitrogen to ecosystems (1 mark).

Answer: Photosynthetic prokaryotes; heterocyst nitrogen fixers such as Nostoc.

Example 4: Mycoplasma · 3 marks · Short answerHarder board level

Mycoplasma is the smallest living cell and is often drug-resistant to wall-acting antibiotics. Explain why, using its structure.

Try it first, then show the solutionSolution

Mycoplasma has no cell wall (1 mark).
Antibiotics that inhibit cell wall synthesis have no target in it (1 mark).
So it is resistant to such drugs, though it can still cause disease in plants and animals (1 mark).

Answer: No wall means wall-acting antibiotics have no target.

Example 5: Sexual reproduction in bacteria · 5 marks · Long answerHOTS / competency

Bacteria lack gametes and meiosis. Why is DNA transfer between them called a primitive form of sexual reproduction, and how does it differ from binary fission in terms of genetic variation?

Try it first, then show the solutionSolution

Fission is asexual: the cell divides into two identical cells (1 mark).
DNA transfer (conjugation, transformation, transduction) moves genes from one cell to another (1 mark).
There are no gametes or fusion of nuclei, so it is not true sexual reproduction (1 mark).
The recipient gets new gene combinations, adding variation (1 mark).
Fission gives clones, so variation arises only through mutation (1 mark).

Answer: DNA transfer introduces variation; fission gives clones.

Where students lose marks in Kingdom Monera: Bacteria

The slips examiners see most often, and what to write instead.

Mistake: Listing cyanobacteria as algae of Plantae
Blue-green algae name misleads.
Wrong working
Cyanobacteria are green algae.
Right working
Cyanobacteria are prokaryotes in Monera.
Do this: Prokaryote means Monera.
Usually costs: 1 mark.
Mistake: Mycoplasma with wall
Wall is assumed for all bacteria.
Wrong working
Mycoplasma has a rigid wall.
Right working
Mycoplasma has no cell wall.
Do this: Smallest and wall-less.
Usually costs: 1 mark.
Mistake: Calling DNA transfer gamete fusion
Sexual is taken literally.
Wrong working
Bacteria form gametes.
Right working
Bacteria transfer DNA; no gametes.
Do this: No gametes in Monera.
Usually costs: 1 mark.

Exam tips

Quote the three archaebacteria groups with habitats.
Name heterocysts and two nitrogen fixers.
Mention both the harm and the use of bacteria in importance questions.
Do not call cyanobacteria algae in the Monera sense.

Practice questions on Kingdom Monera: Bacteria

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Methane-producing bacteria in the gut of ruminants are
(a) halophiles (b) methanogens (c) cyanobacteria (d) mycoplasma
Hint
Biogas.
Answer
(b) methanogens.
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Mycoplasma can survive without oxygen.
Reason (R): Mycoplasma lacks a cell wall.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Two facts, no link.
Answer
(b).
Q3 · 2 marks · Very short answerBoard level
Which cell in Nostoc fixes nitrogen? Why is Nostoc useful in paddy fields?
Hint
Heterocyst.
Answer
The heterocyst. It converts atmospheric nitrogen into usable forms, enriching the soil.
Q4 · 4 marks · Case-basedHarder board level
Read and answer.
Suppose a lab isolates three prokaryotes: X lives in a salt pan, Y has chlorophyll a and heterocysts, Z has no cell wall.
(a) Identify X, Y and Z. (1)
(b) Which is the smallest of them? (1)
(c) Which one would be killed by an antibiotic acting on cell wall? Explain. (2)
Hint
Halophile, cyanobacterium, mycoplasma.
Answer
(a) X halophile (archaebacterium); Y cyanobacterium; Z mycoplasma. (b) Z. (c) Y, which has a normal peptidoglycan wall; Z has none, and X has a different wall structure.
Q5 · 3 marks · Short answerHOTS / competency
Suppose a student argues that bacteria should be called plants because cyanobacteria photosynthesise. Evaluate with two structural reasons.
Hint
Prokaryote versus eukaryote.
Answer
Cyanobacteria are prokaryotes: no nuclear membrane and no membrane-bound organelles such as chloroplasts, unlike plants. Their cell wall is of peptidoglycan, not cellulose. So they belong to Monera despite photosynthesis.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Name the shapes of bacteria.Show answer
Coccus, bacillus, vibrio, spirillum.
2.Which bacteria produce methane?Show answer
Methanogens.
3.Which are the smallest living cells?Show answer
Mycoplasma.
4.What is a heterocyst?Show answer
A nitrogen-fixing cell in some cyanobacteria.
5.What is the cell wall made of in eubacteria?Show answer
Peptidoglycan.
6.How do bacteria mainly reproduce?Show answer
By binary fission.

Kingdom Monera: Bacteria: frequently asked questions

What is kingdom Monera?

The kingdom of all prokaryotes: bacteria, cyanobacteria, archaebacteria and mycoplasma.

How do archaebacteria differ from eubacteria?

They have a special cell wall and live in extreme habitats.

What are heterocysts?

Specialised cells in cyanobacteria such as Nostoc that fix nitrogen.

Why is mycoplasma special?

It has no cell wall and is the smallest living cell.

What is Gram staining?

A stain that divides bacteria into Gram positive and Gram negative by the cell wall.